Preparation method of transparent flame-retardant anti-ultraviolet wood fiber composite material

Abstract

The invention discloses a preparation method of a transparent flame-retardant anti-ultraviolet wood fiber composite material, which comprises the following steps: by taking balsa wood as a template, carrying out decoloration treatment by a sodium chlorite solution, loading carbon quantum dots, taking epoxy resin as filling resin, taking dimethyl methylphosphate as an additive flame retardant, and preparing the transparent flame-retardant anti-ultraviolet wood fiber composite material. The anti-ultraviolet composite transparent wood with excellent optical performance and flame retardant performance is designed and synthesized. An ultraviolet-visible transmittance test shows that the transparent wood added with DMMP can keep good transmittance, the heat conductivity of the transparent wood is reduced, and meanwhile the transparent wood has a good ultraviolet shielding effect. The vertical combustion, limit oxygen index and cone calorimeter test results show that the flame retardant property of the material is obviously improved.

Description

Technical Field

[0001] The present invention belongs to the field of functional biomass fiber composites, and particularly relates to a preparation method of a transparent flame-retardant and ultraviolet-resistant wood fiber composite material. Background Art

[0002] Due to the expansion of the global economy, the demand for energy consumption has increased. Most of the energy currently used is still fossil fuels such as coal, oil, and natural gas, which lead to the generation of greenhouse gases and accelerate global warming. In contrast, biomass fiber is an environmentally friendly material with advantages such as being green and renewable. It is rich and available, has a low price, and degrades naturally. Therefore, making full use of biomass materials can largely solve the problems of energy shortage and environmental pollution and reshape our environment.

[0003] Natural plant fiber is the most sustainable resource in the world and is a natural polymer material with high strength and high rigidity. As the most widely used representative of biomass materials - wood, it is a degradable and renewable environmentally friendly material with unique properties such as easy processing and high strength-to-weight ratio, as well as advantages such as low energy consumption, beautiful texture, and low cost. It is not only the most used bio-based renewable material but also has a wide range of applications in the construction, mining, and architectural decoration industries.

[0004] As a newly emerging carbon nanomaterial, carbon quantum dots (CQDs) have excellent fluorescence properties, low toxicity, and ideal biocompatibility. They have a variety of surface functional groups and internal carbon skeleton structures, are easy to perform surface functionalization and complexation with inorganic, organic, polymer, and bioactive substances, and have a unique strengthening effect on the matrix material. Fluorescent carbon quantum dots can be doped with flame-retardant elements such as nitrogen and phosphorus and have potential flame-retardant application prospects. In addition, because CQDs have the ability to absorb and scatter ultraviolet light, they are considered polymer additives with ultraviolet shielding functions.

[0005] However, due to the flammable nature of wood itself, its scope of use has been greatly restricted. With the development of the wood structure industry in China, more and more wood structure buildings need to be fire-retardant treated. Thus, it is crucial to endow wood with high added value and a wide range of application fields. Transparent wood (TW) has the advantages of high anisotropy, high light transmittance, adjustable light haze, high thermal insulation, high impact energy absorption, and renewability, meeting the increasing performance requirements and the needs of new application scenarios, bringing huge cost savings and long-term environmental benefits, and showing great potential for multifunctionalization. Currently, endowing different properties to transparent wood has become an important research direction. In the relevant technical fields, there have been many patent applications related to the technologies and methods of transparent wood functionalization. For example, adding luminescent and energy storage materials (CN111231034A), selecting colored resins to endow the material with different colors (CN116352830A), gel spraying to obtain superhydrophobic properties (CN116810945A), etc. However, there is currently little work on the preparation of transparent wood with fire-retardant, heat-insulating, and ultraviolet-resistant properties. This work uses fewer raw materials and a simpler design process, providing new methods and ideas for the preparation of transparent fire-retardant and ultraviolet-resistant wood fiber composites. Summary of the Invention

[0006] In view of the deficiencies in the art, the present invention provides a method for preparing a transparent flame-retardant and ultraviolet-resistant wood fiber composite material. Balsa wood, as a material with low density and high porosity, helps the penetration of epoxy resin. It is easy to process, has good mechanical properties, and can have better optical properties after being transparentized. Therefore, it is used as the wood fiber substrate in the present invention. The present invention uses a chemical decolorization method to remove most of the cellulose in the wood. While loading carbon quantum dots, it modifies epoxy resin E135 with an additive flame retardant, dimethyl methylphosphonate (DMMP), so that the wood has excellent flame retardant properties while maintaining a certain transmittance, and can absorb most of the ultraviolet rays. DMMP, as an organophosphorus flame retardant with a high phosphorus content, does not release toxic gases during the combustion process and meets the environmental protection requirements. When it is compounded with epoxy resin, it can bring changes in the interface and microstructure, thereby reducing the thermal conductivity of the system. At the same time, during the combustion process, the N element in the carbon quantum dots is thermally decomposed, and non-combustible gases such as nitrogen-containing small molecules are released, diluting the concentration of combustible gases and reducing the combustion rate. It can cooperate with DMMP to exert a flame retardant effect. The method of the present invention improves the flame retardant properties of the transparent biomass fiber composite material, reduces the fire hazard, and enhances its application potential. The present invention does not add some accessory functions on the basis of transparent wood, but directly prepares a transparent wood integrating the advantages of high transmittance, high flame retardancy, ultraviolet resistance, and low thermal conductivity. Using it as a new material to replace glass can achieve daylighting while shielding most of the ultraviolet rays, reducing the harm of ultraviolet rays to the human skin, and preventing the aging of indoor furniture. At the same time, the characteristic of low thermal conductivity indicates that the material has good heat insulation performance, which helps to achieve the effect of warm in winter and cool in summer indoors. Therefore, in the face of various energy crises today, the present invention provides new ideas for the research and development of environmentally friendly, energy-saving, and safe building materials.

[0007] The method for preparing the transparent flame-retardant and ultraviolet-resistant wood fiber composite material of the present invention includes the following steps:

[0008] Step 1: Using urea and citric acid as raw materials, carbon quantum dots are prepared by a hydrothermal reaction. The carbon quantum dot solution is centrifuged, filtered, dialyzed, and freeze-dried to obtain a brownish powder, which is configured into an ethanol solution of carbon quantum dots.

[0009] Step 2: Prepare an acetic acid buffer solution of NaClO 2 The wood is impregnated in the NaClO 2 solution, heated in an oil bath until the wood turns white, washed several times with deionized water (60 °C), and then stored in the ethanol solution of carbon quantum dots obtained in Step 1 and allowed to stand to complete dehydration and the loading of carbon quantum dots.

[0010] Step 3: Add epoxy resin E135, dimethyl methylphosphonate (DMMP), and curing agent D210 into a reactor, stir at high speed for 5 min until completely and evenly mixed, and remove air bubbles under vacuum.

[0011] Step 4: Immerse the white wood sample obtained in Step 2 in the epoxy resin solution obtained in Step 3, transfer it to a vacuum oven for vacuum degassing and impregnating the wood to fully impregnate the wood with the epoxy resin.

[0012] Step 5: Clamp the sample obtained in Step 4 between two glass slides, wrap it with aluminum foil to complete curing. After curing is completed, carefully peel the synthesized composite material from the glass slides.

[0013] In Step 1, the molar ratio of urea to citric acid is 1:1; the hydrothermal reaction temperature is 160 °C, the reaction time is 12 h. After the reaction ends, cool the reaction kettle for 12 h; set the rotation speed to 10000 r / min and the time to 10 min during centrifugation; use a microfiltration membrane with a pore size of 0.22 μm for filtration; the dialysis bag used for dialysis is 1000 DA.

[0014] In Step 2, the wood is balsa wood with a thickness of 0.5 - 1.0 mm. Different woods can achieve different effects. The reason for choosing balsa wood is that balsa wood has a rich porous structure, which is more conducive to the penetration and filling of epoxy resin and can better achieve the effect of high transparency.

[0015] In Step 2, the 2 mass fraction of the NaClO solution is 4 wt%, and the pH of the solution is adjusted to 4.6 with glacial acetic acid.

[0016] In Step 2, the heating temperature of the oil bath is 80 - 90 °C, and the heating duration is 7 h. As the impregnation time increases, the wood gradually fades from its original log color to white.

[0017] In Step 2, the duration of dehydration by replacement with absolute ethanol is ≥48 h.

[0018] In Step 3, DMMP accounts for 5 wt% - 15 wt% of the total mass of the epoxy resin, such as 5 wt%, 7 wt%, 10 wt%, 13 wt%, 15 wt%.

[0019] In Step 4, vacuum degassing is carried out at room temperature, the degassing pressure is 200 Pa, each degassing lasts for 5 min, and it is repeated 3 - 5 times.

[0020] In Step 5, the curing process is carried out at room temperature and normal pressure for 48 h.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] 1. The preparation method of the transparent flame-retardant and ultraviolet-resistant wood fiber composite material provided by the present invention uses simple raw materials and processes to remove lignin and load carbon quantum dots, and uses the additive flame retardant DMMP to improve the flame retardant effect of the composite material. The carbon quantum dots and DMMP can synergistically play a flame retardant effect, and DMMP can reduce the thermal conductivity of the composite material. In the present invention, balsa wood used as the base material has a rich porous structure, which is conducive to the impregnation of resin and improves the transparency of the composite material. It is a renewable green resource.

[0023] 2. Both urea and citric acid used to prepare carbon quantum dots in the present invention are non-toxic and harmless raw materials, and no harmful by-products will be generated during the preparation process. The cost is low and it is environmentally friendly; the preparation method is a one-step hydrothermal method, the process and operation are simple, and no complex equipment and treatment steps are required.

[0024] 3. In the present invention, the steps of vacuum impregnation and curing of wood only need to be carried out at room temperature, and no special equipment is required, which greatly reduces the cost and energy consumption. It is a green and environmentally friendly process.

[0025] 4. The transparent wood prepared by the present invention is a material that integrates multiple functions, rather than adding additional functions to the transparent wood. Therefore, it can be better used as a multifunctional composite material for in-depth research, providing a better idea for the development of safe and energy-saving building materials. Brief Description of the Drawings

[0026] Figure 1 It is the TEM picture of the carbon quantum dots prepared by the present invention. Among them, a and b are the TEM pictures of the carbon quantum dots dispersed on the molybdenum grid, and c is the particle size distribution diagram of the carbon quantum dots.

[0027] Figure 2 It is the XRD pattern of the carbon quantum dots prepared in the present invention.

[0028] Figure 3 It is the digital photo of the transparent wood composite material of epoxy resin and different addition amounts of DMMP on the school badge of the University of Science and Technology of China in the embodiment of the present invention. From left to right, they are samples of EP, DMMP addition amounts of 5wt%, 7wt%, 10wt% and 13wt% respectively.

[0029] Figure 4 It is the cross-sectional SEM picture of wood at different process stages in the embodiment of the present invention. Among them, a 1 and a 2 are untreated balsa wood (NW), b 1 and b 2 are delignified balsa wood (DW), c 1 and c 2 are transparent wood (TW-CQDs-10%) after the infiltration of epoxy resin with 10% DMMP addition.

[0030] Figure 5 This is the characterization of wood at different process stages in the embodiments of the present invention. Among them, a is the structural formula of lignin, cellulose, and hemicellulose, b is the ATR characterization spectrum of various woods and their composites, and c is the XRD spectrum of wood and its composites.

[0031] Figure 6 This is the transmittance spectrum of different composites in the embodiments of the present invention, covering glass, epoxy, different woods, and their composites. Among them, Figure a shows the transmittance in the ultraviolet-visible light region, and Figure b differentiates the transmittance in the ultraviolet light region.

[0032] Figure 7 This is a digital photo showing the ultraviolet shielding effect of the composite material in the embodiments of the present invention. Among them, a 1 -a 3 is a glass sample, and b 1 -b 3 is a sample of TW-CQDs-10%. Both groups of pictures show the color change of the ultraviolet induction card before and after being irradiated by ultraviolet light for 1 minute, with the sample partially blocking it.

[0033] Figure 8 This is the cone calorimeter curve of the composite material in the embodiments of the present invention. Among them, a is the heat release rate curve of the composite material with different addition amounts of DMMP, b is the total heat release curve of the composite material with different addition amounts of DMMP, c is the smoke release rate curve of the composite material with different addition amounts of DMMP, and d is the total smoke release curve of the composite material with different addition amounts of DMMP.

[0034] Figure 9 This is the thermogravimetric, microcalorimetric test curve, vertical burning, and limiting oxygen index bar chart of the composite material in the embodiments of the present invention. Among them, a is the thermogravimetric curve of the sample under nitrogen, b is the derivative thermogravimetric curve of the sample under nitrogen, c is the heat release curve of the microcalorimetric test of the sample, and d is the bar chart of the limiting oxygen index and vertical burning of the sample.

[0035] Figure 10 This is the bar chart of the thermal conductivity test of the composite material in the embodiments of the present invention. Detailed implementation manners

[0036] To further illustrate the technical solution of the present invention, the preferred implementation manners of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0037] Example 1: Preparation of Carbon Quantum Dot Solution

[0038] 1. Dissolve equimolar amounts of urea and citric acid in deionized water, and ultrasonically stir for 15 min to form a homogeneous solution.

[0039] 2. Transfer the above solution to a stainless-steel autoclave with a polytetrafluoroethylene liner, and hydrothermally treat it at 160 °C for 12 h.

[0040] 3. Add ultrapure water to the product obtained by the above hydrothermal treatment, stir evenly, centrifuge at a speed of 10000 r / min for 10 min, remove the precipitate, and retain the yellowish-brown supernatant.

[0041] 4. Transfer the above supernatant to a 1000 DA dialysis bag and dialyze it in flowing ultrapure water for 48 h.

[0042] 5. Lyophilize the solution after the above dialysis to obtain a brown carbon quantum dot solid powder.

[0043] 6. Disperse the carbon quantum dot solid in an ethanol solution with a concentration of 0.02 mg / mL to obtain an ethanol solution of carbon quantum dots.

[0044] Figure 1 The TEM image of the carbon quantum dots prepared by the present invention shows that the carbon dots are evenly dispersed, and the overall particle size is less than 5.0 nm, concentrated between 1.0 - 2.0 nm.

[0045] Figure 2 The XRD pattern of the carbon quantum dots prepared by the present invention shows an obvious broad peak in the spectrum, corresponding to the diffraction peak of graphene at the (002) crystal plane, indicating that the carbon quantum dots obtained by the experimental process of the present invention have the characteristic crystal structure of graphene.

[0046] Example 2: Preparation of Delignified Wood and Loading of Carbon Quantum Dots

[0047] 1. Dissolve sodium chlorite in deionized water, stir to form a homogeneous solution with a concentration of 4 wt%, and slowly add glacial acetic acid under magnetic stirring to adjust the pH to 4.6 to obtain a light green transparent solution.

[0048] 2. Immerse the cut basswood chips in the above obtained solution, transfer them to an 85 °C oil bath and heat for 8 h, slowly turn on the magnetic stirring until the basswood chips turn white.

[0049] 3. Wash the basswood chips 3 times with 60 °C deionized water to remove NaClO 2 and other impurities.

[0050] 4. Immerse the product in the carbon quantum dot ethanol solution obtained in Example 1 for a soaking time of more than 48 h to displace the residual moisture in the balsa wood and simultaneously load the carbon quantum dots.

[0051] Example 3: Preparation of modified epoxy resin impregnating solution

[0052] 1. Weigh E135 epoxy resin and D210 curing agent with a mass ratio of 10:3, and add DMMP with mass fractions of 5 / 7 / 10 / 13 wt% respectively according to the ratio, and manually stir for 1 min.

[0053] 2. Transfer the above mixed system to a vacuum homogenizer, set the rotation speed to 2000 r / min and the time to 5 min to obtain a uniformly mixed flame-retardant epoxy resin impregnating solution for later use.

[0054] Example 4: Preparation of flame-retardant transparent wood

[0055] 1. Completely immerse the balsa wood loaded with carbon quantum dots obtained in Example 2 in the epoxy resin impregnating solution obtained in Example 3, and transfer it to a vacuum oven.

[0056] 2. Evacuate at room temperature for 5 min and release the air for 5 min, repeat 3 - 5 times to allow the epoxy resin to fully penetrate into the wood.

[0057] 3. Take out the above wood product, wrap it with aluminum foil and clamp it between two glass slides, and cure it at room temperature for 24 h to obtain highly transparent flame-retardant transparent wood.

[0058] Figure 3 Digital photos of the epoxy resin and transparent wood in the embodiments of the present invention on the school emblem picture of the University of Science and Technology of China. From left to right are samples of EP, DMMP added at 5 wt%, 7 wt%, 10 wt% and 13 wt%. The school emblem pattern below the samples can be clearly observed, reflecting the high transparency of the transparent wood.

[0059] Figure 4 Cross-sectional SEM pictures of wood at different process stages in the embodiments of the present invention. The conduit structure in the wood is clearly visible. Removing lignin will not damage this rich pore structure, and the pore structure will be filled with epoxy resin after vacuum infiltration.

[0060] Figure 5 Characterization of wood at different process stages in the embodiments of the present invention. NW and DW both show the peak surface of cellulose in the wood structure. When the epoxy resin penetrates, this peak surface will be covered. When DMMP is added, the degree of coverage of the peak surface is greater. Due to the presence of cellulose, various peaks appear in the infrared spectrum. Among them, at 1509 cm -1 and 1606 cm -1At this point, due to the lack of lignin, the change in the aromatic structure leads to the emergence of new peaks.

[0061] Figure 6 This is the transmittance spectrum of different composite materials in the embodiments of the present invention, showing the transparency of different materials. In the visible light band, the transmittance of glass and epoxy resin is the highest. With the addition of DMMP, the transmittance of TW and its composite materials decreases slightly, and TW with 13wt% DMMP can still maintain at 73.9%. At the same time, in the ultraviolet light band, the loading of carbon quantum dots reduces the transmittance of ultraviolet rays.

[0062] Figure 7 This is a digital photo showing the ultraviolet shielding effect of the composite materials in the embodiments of the present invention, indicating that glass hardly has the function of blocking ultraviolet rays, while the transparent wood in this embodiment can greatly reduce the transmittance of ultraviolet rays.

[0063] Figure 8 This is the cone calorimeter curve of the composite materials in the embodiments of the present invention. Epoxy resin has a high heat release during combustion. The addition of DMMP greatly reduces the peak heat release and total heat release of the material. Among them, TW-CQDs-13% can reduce both pHRR and THR by 40%. At the same time, the action of the condensed-phase flame retardant mechanism causes some of the smoke during the combustion of the sample to be absorbed by the carbon layer, and finally the smoke release amount is also reduced, demonstrating the smoke suppression and toxicity reduction performance.

[0064] Figure 9 This is the thermogravimetric, micro-calorimetry test curves, vertical burning and limiting oxygen index bar charts of the composite materials in the embodiments of the present invention. The addition of DMMP can slightly reduce the thermal decomposition rate, and the results of MCC are consistent with the cone calorimetry test results. When the addition amount of DMMP reaches 10%, the vertical burning grade of the sample can reach V-0.

[0065] Figure 10 This shows the thermal conductivity data of the composite materials in the embodiments of the present invention. It can be seen that the thermal conductivity of transparent wood is much lower than that of glass materials. The increase in the addition amount of DMMP can reduce the thermal conductivity while improving the flame retardant performance of the composite. As an organophosphorus compound, the phosphonic acid groups and methyl and other functional groups contained in the molecular structure of DMMP will interfere with the regularity and order of the epoxy resin molecular chain, thus affecting heat conduction. When DMMP is mixed with epoxy resin, an interfacial region will be formed in the resin matrix. Due to the differences in the molecular structure and thermal properties between DMMP and epoxy resin, a thermal resistance will be generated at the interface, reducing the thermal conductivity of the entire system.

Claims

1. A method for preparing a transparent flame-retardant UV-resistant wood fiber composite material, characterized in that The steps include: Step 1: Using urea and citric acid as raw materials, carbon quantum dots are prepared by hydrothermal reaction. The carbon quantum dot solution is centrifuged, filtered, dialyzed and freeze-dried to obtain a brown powder, which is then configured into an ethanol solution of carbon quantum dots; Step 2: Prepare a NaClO2 glacial acetic acid buffer solution, immerse the wood in the NaClO2 solution, heat the wood in an oil bath until the wood turns white, wash it several times with deionized water, and then store it in the ethanol solution of carbon quantum dots obtained in step 1 and let it stand to complete dehydration and carbon quantum dot loading; Step 3: Add epoxy resin, dimethyl methyl phosphate and curing agent into the reactor, stir and mix evenly, and remove bubbles under vacuum; Step 4: The white wood sample obtained in step 2 is impregnated in the epoxy resin solution obtained in step 3, and then transferred to a vacuum oven for vacuum degassing and impregnation of the wood, so that the wood is fully impregnated with the epoxy resin; Step 5: The sample obtained in step 4 is sandwiched between two glass slides to complete the curing. After the curing is completed, the synthesized composite material is peeled off from the glass slides.

2. The preparation method according to claim 1, characterized in that: In step 1, the molar ratio of urea to citric acid is 1:1; the hydrothermal reaction temperature is 160° C., and the reaction time is 12 h.

3. The preparation method according to claim 1, characterized in that: In step 1, a microporous filter membrane with a pore size of 0.22 μm is used for filtration; and a dialysis bag with a 1000DA is used for dialysis.

4. The preparation method according to claim 1, characterized in that: In step 2, the wood is balsa wood with a thickness of 0.5-1.0 mm.

5. The preparation method according to claim 1, characterized in that: In step 2, the mass fraction of the NaClO2 solution is 4wt%, and the pH value of the solution is adjusted to 4.6 with glacial acetic acid.

6. The preparation method according to claim 1, characterized in that: In step 2, the heating temperature is 80-90°C. As the immersion time increases, the wood gradually fades from its original log color to white.

7. The preparation method according to claim 1, characterized in that: In step 2, the duration of dehydration by anhydrous ethanol replacement is ≥ 48 h.

8. The preparation method according to claim 1, characterized in that: In step 3, dimethyl methyl phosphate accounts for 5wt%-15wt% of the total mass of the epoxy resin.

9. The preparation method according to claim 1, characterized in that: In step 4, vacuum degassing is performed at room temperature, the degassing pressure is 200 Pa, each degassing is 5 min, and it is repeated 3-5 times.

10. The preparation method according to claim 1, characterized in that: In step 5, the curing process is carried out at room temperature and pressure for 48 hours.

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